The snow ski industry makes extensive use of equipment to produce a “man made” snow which approximates the natural snow and allows for a more predictable ski season. In early versions of snow making devices, water and compressed air were mixed internally and then expanded to atmospheric pressure through a nozzle. Subsequent snow maker designs which mixed air and water externally provided better efficiency snow making. In such units, nuclei, or microscopic frozen ice particles, are generated by the expansion of the compressed air. The nuclei are merged with water droplets issuing from pressure atomizing water nozzles. For examples of such devices, see U.S. Pat. Nos. 5,004,151 and 5,823,427 of Dupre, et al., U.S. Pat. No. 5,810,251 to McKinney, and U.S. Pat. No. 6,129,290 to the applicant herein.
The air-water flow characteristics of some commercial snow making units are shown in FIG. 1. The Type KE, KZ and O units, are representative of early units; Type KZ is an internal mix unit. Types H and M represent more efficient modern units. Water flow varies with the number of water nozzles a particular unit has. All units require compressed air, typically at 95 pounds per square inch, gage (psig) or higher. Since compressed air is a major cost, units that operate in the lower right part of the Figure are more desirable.
The full range of air and water combinations shown in FIG. 1 cannot be always used. Any given unit may not produce fully frozen snow under particular atmospheric conditions, even though the units are typically mounted on top of 20 to 35 foot towers, to provide time for the water droplets to freeze. FIG. 2 illustrates the varied typical empirical capabilities of some prior art snow making units, when making good snow. (The invention is also shown.) FIG. 2 shows that, in general, as wet bulb temperature increases, an increasing ratio of air to water is required. When air flow increases for any given volume of water, the cost of generating compressed air for a given amount of snow rises.
The desirable characteristics of the Type L fan type snow maker are due to the use of only a small quantity of high pressure air nozzles to produce nuclei. A flowing mass of cold ambient air is provided by the fan, to cool the droplets and aid in their projection away from the head. However, fan type units have a great number of small water nozzles, are more complicated and costly, and are heavier, than those which operate only with compressed air and atomized water.
As indicated by the diversity of patents, and by the diversity of equipment in the field, there is a continuing search and need for snow making devices which have favorable air-water ratios, and which are good at producing snow when the environment is difficult, e.g., when wet bulb temperature approaches the freezing point. And, of course, any snow making device must be sturdy, durable, not prone to icing or clogging, and in general, reliable.